High silica glass



Patented Dec. 1, 1942 men SILICA cuss Martin Emery Nordberg and Harold Edward Rumenapn, Corning, N. Y., assignors to Coming Glass Works, Corning, N. Y., a corporation of New York No Drawing. Application November 18, 1938,

Serial N0. 241,274

9 Claims. (Cl. 49-92) In the prior Patent No. 2,106,744, issued February 1, 1938, to Harrison P. Hood and Martin E. Nordberg, there is disclosed a method of making a highly siliceous glass which comprises melting a glass, fabricating the same into a fixed shape, heat treating the shaped article to separate the glass into a soluble and an insoluble phase, or in other words, to make soluble a major portion of the constituents other than silica, dissolving out the soluble phase or constituents to leave a highly siliceous, rigid, porous structure having the same shape as th initial article and firing the resultant article to close the pores and form a vitreous transparent glass. Such glass has a silica content of over 93% and a thermal expansion coeflicient from about .017 to about .0614 or only slightly above that of pure vitreous silica. As shown in the patent, any coloring oxides or agents present in the initial glass are substantially removed during the process and the final glass is practically colorless.

It is the object of this invention to introduce into such finished glass an inorganic coloring material which will substantially alter the spectral characteristics of the glass without substantial change in heat resistance, thermal expansion coefficient and other valuable properties thereof.

The above and other objects may be accomplished by practicing-our invention which embodies among its features incorporating a salt of a metal which will color glass or fluoresce therein within the pores of the article after the soluin accordance with the above described method,

and thereafter firing it. Another feature comprises incorporating suc metal salt in a restricted portion of the article to form a colored design within the body of the glass as by printing or stamping a solution of the salt on the porous glass in the desired design.

A further feature comprises a glass article containing silica, boric oxide and alkali, in at least a portion of which the silica is over 93%, the boric oxide is under 6% and the alkali is under 1%, said portion being vitreous and non-porous and containing also suiiicient inorganic coloring material to produce color or fluorescence therein.'

In practicing our invention the article is fabricated in the usual manner from a glass containing 60% to 82% SiO2, 20% to 35% BzOaand 5% to alkali oxide, the composition being governed by considerations set forth in the above mentioned patent. In these glasses alumina may amounts up to 4% in glasses of low silica connecessary to cause the required change in structure. As a result of the heat treatment the glass will become more or less completely separated or formed into two phases, one of which is very rich in boric oxide and alkali and is soluble in acids and the other of which is very rich in silica and is substantially insolublein acids. In other words, a change has taken place in the structure of the glass so that theconstituents other than silica are for the most part soluble in acids and may be extracted thereby.

The previous thermal history of a glass has a bearing upon the heat treatment which may be required for best results. Articles which are relatively thick receive some heat treatment in normal working and cooling and the additionalheat treatment required may be difierent from that required by a thinner article which was cooled more quickly during manufacture. Hence the term fhe'at treatment as used herein includes heat treatment during fabrication as well as any additional heat treatment following fabrication.

In ordertthat the leaching step may be carried out with better facility it is desirable, particularly in the case of pressed ware, to etch off the surface of glass by immersing :it for a few minutes in a dilute solution of hydrofluoric acid or in a hot ;5 sodium hydroxide solution.

The article is then rinsed and immersed in-dilute hydrochloric, nitric, or sulfuric acid, the temperature of the bath'being held preferably at or near its boiling point to obtain maximum speed of, extraction. The progress of the extraction may be observed because the interface between the extracted and unextracted portions ofthe glass is visible. Instead of carrying the extraction to completion, it maybe stopped when any desirable depth has-been reached by After the acid treatment the glass is washed to remove all traces of the soluble constituents which have been acted on by the acid. This is best accomplished by immersing the glass for several hours in pure running water so as to expose all sides of the article to the washing action.

The removal of the soluble phase leaves the silica be present in small amounts and its. presence in P ase a a rigid r c ure possessing the crisins] shape of the article, but submicroscopically porous, the pores being filled with water.

We have discovered that metal salts or compounds can be introduced in c, uniform distribution throughout the pores or confined to a limited portion thereof after which the article can be dried and fired to close the pores and produce a non-porous, vitreous glass article having the shape of the initial glass article though somewhat smaller in size and having, in those portions containing the metal, a selective spectral transmission or color. If the whole article is to be colored, this is best accomplished by immersing the washed porous article in a solution of the desired metal salt for a time suflicient to permit the salt solution to diffuse into the pores. An immersion for two hours was sufiicient for complete diffusion into a slab of the porous material one-eighth inch in thickness. This diffusion was about ten times as rapid when a previously dried sample was used. If it is desired to restrict the area of the glass to be colored as for the purpose of forming a design, the article is first dried and the metal salt solution is then applied in the desired design by means of a brush or a stamp or a silk screen or the like. For this purpose the viscosity of the solution may be increased by the addition thereto of a viscous liquid such as glycerine. 7

After the porous glass has been impregnated with the metal salt, it is dried by evaporating from the pores the solvent in which the metal salt was dissolved. In doing this, a moderate heat may be employed, but care should be exercised against expelling the solvent too rapidly because an explosive evolution of the vapor may cause the article to spall or crack. After drying, the temperature is increased to 900. C.-1150 C. where it is held for a short time after which the article may be cooled as rapidly as desired.

Our researches show that practically any colored cation can thus be introduced into the pores and the article thereafter fired to a non-porous colored glass. It has further been found that for a given firing temperature, if an excessive amount of the metal salt is used, the resulting colored glass will not be transparent but will be a colored opal glass, that is, will have light diffusing characteristics. The higher the maximum temperature at which the article is fired, the greater the amount of metal salt that must be introduced to cause opalescence. Articles having a shape which permits their being supported against warping or deforming may be fired at temperatures ashigh as 1300 0., while articles which are subsequently worked in a flame may attain temperatures above 1500 C. The amount of the salt which is absorbed is easily controlled by varying the concentration of the salt'in the solution into which the porous glass is immersed. The maximum concentration which will produce a transparent colored glass will not only depend upon the temperature of firing but will vary with salts of diiferent metals and will vary also with different salts of the same metal. For'example,

thereafter fired at 1150 C., the following table shows the maximum concentrations in weight percent of the respective salts which produced a transparent colored glass and also the corresponding concentrations in terms of the oxide of the respective metals and the color of the resulting glass.

Concentrat on 5 Metal salt perb cent g ggz Color of glass Y weight Cll(N0a)z.3H20 9 2.97 CuO. Olive green.

10 Fe(N 5 .99 F620; Reddlsh orange.

Nl(NOs)z.6H2o 3 .77 Ni0 Rose. C0(NOs)2.6HzO 10 2.58 COO Blue. CoClzJiHzO" 12 3.78 000 Do. Gr(SO4)a.15HzO 3 1.26 CrzOz Yellowish green. CF03 1.3 1.0 CHO: D0.

15 From the above it will be noted that not only do the concentrations of the solutions in terms of oxide vary with respect to the metal employed but, also, as is shown in the cases of cobalt and chromium, the oxide concentrations vary with respect to the particular salt of the metal. This phenomenon is not understood, but is believed to be caused by a selective absorptive efiect of the anion of the respective salts. The above recited maximum concentrations for producing transparent glasses at a firing temperature of"1150 C. are increased somewhat when a firing temperature of,1300 C. is employed. For example, the maximum concentration of nickel nitrate for a firing temperature of 1300 C. is about 10% by weight, for copper nitrate a little over 13%, for cobalt nitrate over 12%, for cobalt chloride 13%, for ferric nitrate over 15%, etc. The color or hue which is produced by a given metal in the finished product is substantially the same whether the nitrate, chloride, or sulphate is used. The color saturation or density varies directly with the concentration of the coloring ion. In other words, various salts of the same metal will produce substantially the same hue but the saturation or density of the color will decrease as the solutions are made more dilute. The chromium compounds, CrOu, NH4Cr(SO4) 2, C12(SO4)1, NH4CrO4, and CrCh in water solutions containing each an amount of the respective salt equivalent to 1% by weight of CrzOa, produced each substantially the same hue in porous glass plates treated therewith and fired.

Obviously the porous glass may also be treated in a solution containing a combination of two or more metal salts and thereafter dried and fired to produce a glass colored by the combination of metals. For example, pieces of porous glass were treated with solutions containing both copper nitrate and cobalt nitrate. The resulting colors were different from those produced by either copper alone or cobalt alone. The ratio of copper to cobalt determines the particular hue which is obtained.

The glasses resulting from treatments with the solutions shown in the above table are all transparent but with solutions of these salts in concentrations greater than above set forth the resulting glasses will be opal and will have light diiiusing characteristics. For some purposes light diffusing characteristics are desirable, but if it is desired to obtain a greater saturation or density of color than can be obtained with the above recited maximum concentrations, we have found that this can be accomplished by introducing into the glass along with the metal salt solution a solution of another salt or compound, hereinafter called clearing agent, which has the effect of increasing the amount of metal salt that can be introduced without causing opalescence. The

number of compounds which have a clearing efasoavee feet is very limited and we have found that. aluminum nitrate, phosphoric acid, and alkali salts possess this property in substantial degree. Presumably other salts of aluminum will also" be effective and we have found that alkali phosphates, such as sodium dihydrogen phosphate, are very eflicient. The presence of P205 in the glass may also have an effect on the ultimate color. It tends to bleach the color of iron and it causes a change in hue of the colors produced by nickeland cobalt. Alkali salts in general-tend to cause devitrification and spelling of the glass on firing due to the tendency of such salts, when too concentrated, to creep or come to the surface on drying.

The following experiment illustrates the efiect of aluminum nitrate and phosphoric acid as clearing agents.

Three plates of the above described porous glam were treated as follows:

One was immersed for 24 hours in a water solution containing by weight of fired at 1150 C. After firing, this sample was" transparent and the color density was considerably greater than that produced b the maximum concentration recited in the above table.

The third sample was immersed for the same length of time in a water solution containing the same percentage of nickel nitrate and containing also an amount of HaPOr, equivalent to 5% by weight of P205, and was thereafter'ufired at 1150 C. After firing, this sample was transparent and although the color saturation was greater than that of the maximum concentration of the above table the hue was different, being in this instance a bright amber yellow.

Subsequent analysis of the samples showed that the first contained .42% NiO, the second contained 56% N10, and the third contained .4l% NiO, thus demonstrating that the effect of the aluminum salt. or the phosphoric acid was not to reduce the amount of nickel ion adsorbed by the porous glass but to exert some specific clearing action. e

If porous glass articles after treatment with a metal salt solution are fired in a reducing atmosphere, unusual color effects can in some cases be obtained. Under strgng reduction most metal salts in such glasses are reduced to metal and give the glass a smoky black "appearance. Some metals, however, produce a useful and unique coloration. For example, a glass that has been treated with a solution of a molybdenum salt, whenfired in an atmosphere of hydrogen, becomes a lustrous, glossy, opaque black throughout its mass. A glass treated with a vanadium salt and fired in hydrogen takes on a beautiful sky blue hue.

We have found that, if desired, the absorption or introduction of the metallic salt solution into the porous glass can be confined to any particular area of the article to produce therein any desired design. This is accomplished by increasing the viscosity of the solution by the addition of a viscous liquid such as glycerine and applying the viscous solution to the selected areas by means of a brush or a stamp. The well known silk screen process may also be employed for this purpose. Best results are obtained by first drying the porous glass before solution. In this manner various intricate designs and decorations may be formed within the surface of the article in which several colors may appear due to the successive application of different metal salts. An article may thus be produced which is of one color on one face and a different color on its other face.

Glasses which have been prepared in accordance with the above described method show the characteristic fluorescence of the metal which was introduced when such glasses are irradiated with ultraviolet light and ,other exciting radiations. It will thus be seen that fluorescent screens can be prepared in which intricate multicolored designs can be caused to change intermittently in color and appearance by alternately transmitting visible and ultraviolet light therethrough.

We claim: i

1. A shaped article of glass containing silica, boric oxide and alkali, in at least a portion of which the silica is over 93%, the boric oxide is under 6% and the alkali is under 1%, said portion being vitreous and non-porous and containing also sufiicient inorganic coloring material to produce coloration therein.

2. A shaped article of glass containing silica, boric oxide and alkali, the silica being over 93%, the boric oxide under 6% and the alkali under 1%, the glass being vitreous and non-porous and containing also sufiicient inorganic coloring material to produce coloration therein.

3. A shaped article of glass containing silica, boric oxide and alkali, the silica being over 93%, the boric oxide under 6% and the alkali under 1%, the glass being vitreous and non-porous and containing also a coloring metal in an amount sufficient to produce substantial coloration theree 4. A shaped article of glass containing silica, boric oxide and alkali, the silica being over 93%,

the boric oxide under 6% and the alkali under 1%, the glass being vitreous and non-porous and containing in different portions of its mass a coloring metal in an amount sufficient to produce substantial coloration.

5. A shaped article of glass containing silica,

boric oxide and alkali, in at least a portion of which the silica is over' 93%, the boric oxide is under 6% and the alkali is under 1%, said portion being vitreous and non-porous and containing also nickel in an amount suflicient to produce substantial coloration therein.

6. A shaped article of glass containing silica,

boric oxide and alkali, in at least a portion of which the silica is over 93%, the boric oxide is under 6% and the alkali is under 1%, said portion being vitreous and non-porous and containing also cobalt in an amount suiflcient to produce substantial coloration therein.

'l. A shaped article of glass containing silica, boric oxide and alkali, in at least a portion oi which the silica is over 93%, the boric oxide is under 6% and the alkali is under 1%, said portion being vitreous and non-porous and containing also chromium in an amount sufficient to produce substantial coloration therein.

8. A shaped article of glass containing silica, bo'ric oxide and alkali, the silica being over 93%, the boric oxide under 6% and the alkali under 1%, the glass being vitreous and non-porous and containing also a coloring metal in an amount the application of the sumcient to produce substantial coloration theretion being vitreous and non-porous and conin and a small amount of phosphorus. taining also nickel in an amount sufflcient to 9. A shaped article of glass containing silica, produce substantial coloration therein and a boric oxide and alkali, in at least a portion of small amount of phosphorus.

which the silica is over 93%, the boric oxide 5 MARTIN EMERY NORDBERG.

is under 6% and the alkali is under 1%, said por- HAROLD EDWARD RUMENAPP. 

